From antiferromagnetic and hidden order to Pauli paramagnetism in UM2Si2compounds with 5felectron duality

Abstract

Using inelastic X-ray scattering beyond the dipole limit and hard X-ray photoelectron spectroscopy we establish the dual nature of the U5felectrons in UM2Si2(M = Pd, Ni, Ru, Fe), regardless of their degree of delocalization. We have observed that the compounds have in common a local atomic-like state that is well described by the U5f2configuration with theΓ1(1)andΓ2quasi-doublet symmetry. The amount of the U 5f3configuration, however, varies considerably across the UM2Si2series, indicating an increase of U 5f itineracy in going from M = Pd to Ni to Ru and to the Fe compound. The identified electronic states explain the formation of the very large ordered magnetic moments inUPd2Si2andUNi2Si2, the availability of orbital degrees of freedom needed for the hidden order inURu2Si2to occur, as well as the appearance of Pauli paramagnetism inUFe2Si2. A unified and systematic picture of the UM2Si2compounds may now be drawn, thereby providing suggestions for additional experiments to induce hidden order and/or superconductivity in U compounds with the tetragonal body-centeredThCr2Si2structure.